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Specular shimmer on edges of normal mapped object

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3 comments, last by cozzie 4 years, 5 months ago

Hi all,

I've got a shader which does normal mapping in a standard way, and adds specular highlights as you'd expect as well. I would post the code, but I don't think there's anthing particularly special about it.

I like the effect, but there's a little problem when I'm looking at an object with the light directly behind it. The edges of smoother parts of the model appear to have a shimmering effect where specular highlights wrap around the edge, as seen on the legs and other areas of the model below:

Does anyone know if there's a quick fix for this?

Thanks!

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Maybe normals that point away because of approximation error from triangle interpolation cause some kind of math bug in your code?

You could try using Blinn-Phong rather than (what appears to be) Phong:

vec3 reflectVec = reflect(-lightDir, normal);
vec3 spec = pow(max(dot(reflectVec, viewVec), 0.0), 5.0);

Another (albeit significantly more complex) way you could resolve this artifact is by using some form of anti-aliasing. Some techniques don't handle "specular aliasing" as this artifact is referred to, but techniques like Temporal Anti-Aliasing do.

I recall having this effect a number of times. In my case the cause were normals that didn't all point in the same direction. I'm not sure if there's a quick fix for it. Either anti-aliasing as mentioned (but I doubt that), or maybe a different shadowing approach. Should these pixels actually be lit or in shadow?

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